Compositions containing benzothiazyl disulfide diarylguanidine



Patented July 12, 1949 COMPOSITIONS CONTAINING BENZOTHIA- ZYL DISULFIDE DIARYLGUANIDINE Arnold R. Davis, Riverside, Conn., assignor to American Cyanamid Company, New .York, N. Y., a corporation of Maine No Drawing. Application February 8, 1945, Serial No. 576,909

6 Claims.

This invention relates to a novel vulcanization accelerator, to rubber compositions containing the same and to methods of vulcanization using these accelerators. More specifically, the invention relates to novel activated accelerators which constitute fusion products of benzothiazyl disulfide and a diarylguanidine.

For many years, natural rubber and, more recently, synthetic rubber has been vulcanized using as the accelerator benzothiazyl disulfide activated by a diarylguanidine and metal oxides, such as zinc oxides and the like. Benzothiazyl disulfide produces excellent results so far as the physical properties of a pr perly finished product are concerned. While its use has been quite extensive, improvements have been constantly sought.

Benzothiazyl disulfide has only a very low solubility, less than 0.5%, in rubber at ordinary room temperatures. This leads to a number of difficulties. Compounds which have such limited solubility in rubber as exhibited by benzothiazyl disulfide are extremely difficult to disperse uniformly in the composition. This has the unfortunate efiect of producing uneven cures. Poor accelerator distribution results in non-uniform test results and erratic performance in service. This difficulty is aggravated by the ordinary procedure in the plant. Rubber compositions during milling are at elevated temperatures, usually above 60 C. and often at about 100 to 160 C. While the benzothiazyl disulfide may be thoroughly dissolved in the rubber at the high temperature, it is precipitated out When the material cools. In some cases, crystals may even be observed at the surface.

When a compound such as benzothiazyl disulfide is used with another compound to form the actual accelerator, as in the present instance it is used with a, diarylguanidine, still further difficulties are encountered. Not only is the material poorly distributed, but, because of the heterogeneous mixing, the chemical reaction between the components of the accelerator is also indifferently accomplished. Again, wide variations in tensile strength, elongation and other physical properties are to be noted in test samples and the products are erratic in service.

It is, therefore, the principal object of the present invention to provide a novel accelerator which will possess the natural advantages inherent in the use of activated benzothiazyl disul- 2 fide without being subject to the difliculties encountered when the latter is used per se with activators. It is also an object of the present invention to provide an accelerator which is simply and readily made, which is easily compounded with the vulcanizable composition, and which gives uniform and improved physical properties to the vulcanized product.

In general, the desired objects of the present invention are simply and easily accomplished by recognizing that the essential difficulty is either one of distributing or one of forming the accelerator in the compound. The distributional difiiculties are overcome by the use of the novel activated accelerators of this invention. The latter constitute amorphous chemical reaction products obtained by the fusion of benzothiazyl disulfide anda diarylguanidine in which the aryl group is mononuclear.

The diarylguanidine used in preparing the novel accelerators of the present invention is not necessarily limited to any particular choice. Excellent results are obtained, for example, using such mononuclear substituted guanidines as diphenyl guanidine, the 'di-toly1 guanidines, phenyl, o-tolyl guanidine, and the dixylyl guanidines. In

, choosing the particular guanidine to be used, certain precautions should be noted. The dixylyl guanidines when fused alone with benzothiazyl disulfide yield products which exhibit definite crystal phases. Diphenyl guani-dine if heated alone with benzothiazyl disulfide at too low a temperature may yield a product showing some crystalline phases. While the formation of crystal phases shows the products are actually chemically combined and not simple mixtures, in use, crystalline forms are not as satisfactory as the amorphous forms. The other diarylguanidines produce substantially amorphous fusion products and cause no trouble in this respect. Where the use of dixylyl guanidines is desirable, the tend- ,ency toward crystallization can be readily eliminated by using them in admixture with another diarylguanidine, preferably a ditolylor a phenyl, tolyl guanidine.

The exact proportions of benzothiazyl disulfide of diarylguanidine used is not wholly critical. In the experimental work done in the development of the accelerators of the present invention, the most preferable results were obtained using a molal ratio of 1:2. These proportions 113.150 simplify calculation when it is desirable to am ss fide are readily combined. When combined, the

product has excellent properties. These proportions, however, may be Varied by a few percent in either direction without necessarily producing an adverse effect on the Vulcanized product. The preferred amorphous products have shown complete solubility even when used to the extent of 3% on the rubber.

Actual preparation of the novel accelerators "of the present invention is quite simple. The selected materials, usually in commi'nute'd form, are admixed, the mixture is heated to the fusion temperature and the temperature is held at that point for a short time. The 'mixture becomes fluid before the maximum temperature is reached. After a few minutes at fusion temperature, the fluid becomes a clear liquid, indicating the occurrence of some chemical change. Fusion temperatures of 120-150 C. normally cover the expected range.

With the exception of the use of dixylyl guanidines alone, or the use of :diphenyl guanidine at too low a temperature, all the fusion products on cooling yield clear, resinous products, which are free from crystalline material. After cooling, all the amorphous products soften at a lower temperature than that at which the mixture of original materials became fluid.

While its exact nature is not wholly understood, the fact that a chemical change occurs during fusion is evidenced in several ways. First, as noted above, the fluent material becomes clear during fusion. Second, the fusion product is completely soluble in rubber, whereas only the diaryl guanidine component of a mechanical mixture dissolves freely, only a small amount of the benzothiazyl disulfide going into solution. Third, a composition containing the fusion product, after'curing, possesses much better physical properties than those of vulcanizates fromcompositions containing only a mechanical mixture.

The invention will be more fully described in conjunction with the following specific examples which are illustrative only and not by way of limitation. All parts are by weight unless otherwise noted. In the examples, the following symbols are used:

BTDS=benzothiazyl disulfide DPG :diphenyl guani'dine DOTG= di-o-tolyl guanidine DXG :dixylyl guanidines POTG=phenyl,o-tolyl guanidine GR-S :Grovernment Rubber-styrene EXAMPLE 1 dence of crystal phases was present after long standing.

EXAMPLE 2 Example 1 was repeated, heating the mix to 150 C., in 23 minutes'al'id holding it at 145150 C. for 5 minutes, the "cooled product was'found to be amorphous, softening at 52--57'C.

EXAMPLE -3 Two -mol parts -of *DOTG we're fused at about 130 C. with one mol part of BTDS. The resultant product was an amorphous resin softening at 60-65 C. and free from crystalline material.

EXAMPLE 4 One mol part of DOTG and one mol part of DPG were fused at about 130 C. with one mol part of BTDS. The resultant product was an amorphous solid softening at 57-62 C.

EXAMPLE 5 One mol part each of DPG, DXG and BTDS were mixed and heated to about 130 C. over 15 minutes and then held at -130 C. for 5 minutes. The clear amorphous product softened at 63-68 C.

EXAMPLE 6 One mol part each of DOTG, DXG and BTDS heated to C. in 20 minutes and held at that point for about -5 minutes yielded a product on cooling which was amorphous and softened at 64-69 C.

EXAMPLE. 7

One mol 'part each of DPG, PO'IG and BTDS heated to 140 C. in 20 minutes and held at -C. for five minutes and cooled produced an amorphous product softening at 56-61 C.

held at 125 C. for 10 minutes gave on cooling an amorphous product melting at 59-64 0.

EXAMPLE 9 A mixture of one mol part each 'ofDXGand 'BTDS was heated to 150C. in 17 minutesan'd held at 150 C. for 8 minutes. The resultant liquid was clear in a thin film but 'aftercool- 'ing a considerable quantity'of fine crystals was apparent. The product softened at about 66 71 C.

EXAMPLE 10 The acceleratoractivity of the products ofthe present invention may be illustrated as follows. Two portions-of a butadiene-styrene copolymer synthetic rubber (GR-S) were compounded and vulcanized, and the resultant physical properties -of the vulcanizate tested. In the first, the fusion product obtained in Example 3 was used as the accelerator, and inthe second, a diphenyl guanidine-benzothiazyl disulflde'fusion product of Example 1 was used. The composition and the resultant properties of the vulcanizat'e are shown in the following-table:

Table I Compounds GR-S 100, I00 EPO Black 50 50 Zinc Oxe '5' 5 Sulfur -2 2 Petroleum Hydrocarbon Softener .10 10 DOTG-BTDS FusiOnPlOd.-- 1.20 A. DPG-BTDS-Fusion Prod 1.30 Set-up Tests Williams 3 min. Y at -100 C. inches No Heat. 0. 116 ;0. After 2.5 hrs. in Boiling H2O 0.146 0.1 52 Ghange,=per cent +26 +32 SHORE HARDNESS Minutes cure sat-141C (O.5-30Idwe1l) so 60,51, 60 53 65956 "64- 57 P651 57. "65 .57

PHYSICAL TESTS 60 Cure at 141 C.

Modulus at 200 per cent Elongation 1 475 500 Tensile strength 1 2, 900 3, 225 Elongation, per cent.. 620 625 Set; per cent 25 25 Torsional hysteresis at 280 F 0. 148 0. 150

After 48 hrs. Aging at 100 0.

Modulus at 200 per cent E1ong. 1. 050 1, 025 Tensile strength 1 2, 750 2,825 Elongation, per cent 520 400 1 Modulus and Tensile in lbs/sq. in. 2 Set at Break 2 min. after break.

, EXAMPLE 11 A similar procedure was carried out on a third sample, using as the accelerator a fusion product obtained according to Example 4. The proportions used and the results obtained are shown in the following table:

PHYSICAL TESTS 60 Oure at 141 0.,

Unaged Modulus at 200 per cent Elongation.. 575 Tensile strength. 3, 350 Elongation, per cent 625 Set, per cent. 28

After 48 hrs. Aging at 100 0.

Modulus at 200% Elong 1, 400 Tensile Strength 3, 200 Elongation, per cent 380 The unpredictable benefits obtained by reacting the components of the activated accelerator before the rubber compounding is readily illustrated by the following example:

EXAMPLE 12 Three additional samples of GR-S were compounded. In the first of these samples, the activator and the accelerator were separately added. In the second, a fusion product prepared according to Example 2 was used, and in the third, a phenyl-o-tolyl guanidine benzothiazyl disulfide fusion product was used. In order that the unreacted components be given the most favorable opportunity to react in situ, the powders were very thoroughly mixed before being added 6 to the composition. The proportions and the physical properties of the resultant vulcanizates are shown in the following table, which very excellently illustrates the advantage of using the products of the present invention.

Table III Compounds oleum carbon Softens DPG-DOTG-BTDS Mech. Mix DPG-DOTG-BTDS Fusion Pro POTG-BTDSFusiou Prod 1 Set-up Tests Williams 3 min Y" at 0. inches No Heat 104 105 104 After 1.5 hr. in Boiling H2O. 144 131 Change, percent... +38 +24 +26 SHORE HARDNESS 45 Minutes Cure at 141 C 65-59 65-58 64-57 TENSILE TESTS 45 Cure at141 0.,

Unaged Modulus 1 750 725 700 Tensile Strength 2, 400 2, 900 2, 800 Elongation, percent 435 520 505 After 48 hrs. A ging at Modulus 1, 225 1, 200 1, 200 Tensile Strength..- 2, 275 2, 675 2, 575 Elongation, percent 315 370 350 (The lowest percent change in the Y" value indicates the lowest tendency to scorch of preoure.)

1 Modulus (at 200 percent elong.) and tensile in p. s. i.

While the foregoing discussion has been largely limited to examples using synthetic butadiene-styrene copolymer type rubbers, this has been simply for illustrative purposes. The novel accelerators of the present invention and the use thereof are applicable not only to synthetic vulcanizable copolymers other than the butadiene-styrene copolymers but also to natural vulcanizable rubber. This is illustrated in the following example.

EXAMPLE 13 A procedure similar to Example 5, using natural rubber and an accelerator produced according to Example 2 was carried out. The proportions used and the properties of the product are shown in the following table.

Table IV Natural rubber 100 Whiting 70 Clay 9 Furnace black 8 EPC black 2 Asphalt base oil 3 Zinc Oxide 5 Sulfur 2.25 DPG-DOTG-BTDS fusion prod. 1.35

TENSILE TESTS 25 cure at 130C. Modulus at 300% 1 850 Tensile strength 2825 Elongation, per cent 560 1 Pounds per Square inch While in the foregoing discussion the improved accelerators of the present invention have been used alone as the sole organic acceleratin agent, these products may be used in conjunction with the standard organic accelerators and/or activators if sov desired. The novel accelerators of this invention may be supplemented or partially replaced by previously known accelerators, for example, benzothiazyl dis-ulfide itself. However, the latter should not be used in amounts exceeding the solubility of the accelerator itself in rubber at ordinary room temperatures. This practice may be illustrated, by the procedure of the followingexample:

EXAMPLE 14 Table V Compounds Zinc Oxide. Sulfur Coal Tar Softener DOTG-DPG-BTDS'Fusion Prod BTDS PHYSICAL TESTS -60 Curse at 141.

Modulus at 300% 1 950 1, 000 Tensile Strength 1 3,250 3, 350 Elongation, Percent 650- 645 1 Pounds per square inch.

Iclaim:

1. A novel vulcanizable composition comprising an unvulcanized sulfur-vulcanizable rubber, selected from natural rubber and synthetic, sulfurvulcanizable copolymer rubbers, sulfur, an accelerator comprising an amorphous reaction product prepared by fusing at 1201-50 0., about 1 mol part of benothiazyl disulfide, with substantially one molecular equivalent by weight of a substituted guanidine having the formula ArG-Ar' in which Ar and Ar represent mononuclear aryl radicals and G represents the guanidine residue and substantially one molecular equivalent by weight of a substituted guanidine having the formula Ar"-G-Ar"' in which Ar and Ar represent mononuclear aryl radicals other than xylyl.

2. A novel vulcanizable composition comprising an unvulcanized, sulfur-vulcanizable rubber, selected' from natural rubber and synthetic, sulfurvulcanizable copolymer rubbers, sulfur, an accelerator comprising the amorphous, low-soften- Number 8 ing point, reaction product,-prepared by fusing at-150 C. 1 mol part of benzothiazyl disulfide with about 2 mol parts of di-o-tolyl-guanidine.

3. A novel vulcanizable composition comprising an unvulcanized, sulfur-vuloanizable rubber, selected from natural rubber and synthetic, sulfurvulcanizable copolymer rubbers, sulfur, an accelerator comprising the amorphous, low-softening-point, reaction product, prepared at 120-l50 C. by fusing lmol part of benzothiazyl disulfide with about one mol part of di-o-tolyl ,guanidine and about one mol part of diphenyl guanidine.

4. A novel vulcanizable composition comprising an unvulcanized, sulfur-vulcanizable rubber, selected from natural rubber and synthetic, sulfurvulcanizable copolymer rubbers, sulfur, an accelerator comprising the amorphous, low-softening point, reaction: product,.preparedby fusing at 120 C. 1 mol-part of benzothiazy-l disulfide with substantially two molecular equivalents by weight of phenyl,o-tolyl guanidine.

5. In a process of producing improved vulcanizates the steps of compounding a mixture comprising an unvulcanized, sulfur-vulcanizable rubber, selected from natural rubber and synthetic, sulfur-vulcanizable copolymer rubbers, sulfur and comprising an amorphous reaction product prepared by fusing at 120-l50 C. about onemol part of benzothiazyl disulfide, with substantially one molecular equivalent by weight of a substituted guanidine having the formula.Ar'--G.--Ar' in which Ar and Ar represent mononuclear-aryl radicals and G represents the guanidine residue and substantially one molecular equivalent. by weight of a substituted guanidine havingthe" formula Ar"'G-Ar" in which Ar'and' Ar represent mononuclear aryl radicals other than xylyl, and subjecting the. compounded mixture to sufficient heat to effect vulcanization.

6. Vulcanizates prepared by admixing an unvulcanized, sulfur-vulcanizable rubber, selected from natural rubber and synthetic, sulfur-vulcanizable copolymer rubbers, sulfur and an ac- 1 celerator comprising an amorphous reaction product prepared by fusingat about l20'-150 C. about one mol part of benzothiazyl-disulfide with substantially one molecular equivalent by Weight of a substituted guanidine having the formula ArGAr' in which Ar and Ar" represent mononuclear aryl radicals and G- represents the guanidine residue and substantially one molecular equivalent by Weight of a substituted guanidine having the formula ArGAr"' in which Ar" and Ar' represent mononuclear aryl radicals other than xylyl, and subjecting the. compounded mixture to sufiicient heat to effect vulcanization.

ARNOLD R. DAVIS;

REFERENCES GI'IED The'following 'referenices are of record in the file of this patent:

FOREIGN PATENTS Country Date 413,296 Great Britain July-1'0; 1934 

